The present invention relates in general to interior trim panels for transportation vehicles, and, more specifically, to a trim panel and manufacturing method to provide a contoured panel shape with an undercut edge without adding expensive or complex manufacturing equipment.
Interior trim panels for cars, trucks, and other transportation vehicles are designed to be both functional and stylish. As a result, complex contoured surfaces are often utilized in designing vehicle interior surfaces.
A typical interior trim panel surface may comprise an instrument panel, dashboard, or door panel formed as a generally thin wall having various features such as mounting extensions for attaching the panel to a vehicle frame and apertures and/or mating bosses for attaching various accessories to the trim panel. For mass-produced vehicles, trim panels are typically made from plastic materials that are injection molded with a generally uniform thickness. The uniform thickness achieves uniform cooling of the plastic material to avoid sags or other distortions in the panel that would result if some portions of the visible surface cooled faster than others. Mounting extensions such as clip towers add thickness to a panel but have a sufficiently small profile on the visible surface to leave the wall generally unaffected.
The molded panel (also known as a substrate) has what is known as a Class A surface facing the vehicle interior so that it is visible to the vehicle occupants and what is known as a Class B surface on the opposite or rear side. A smooth, well-controlled Class A surface is critical to obtaining a quality appearance. To obtain certain curved or sculptured surfaces, complex tooling with many movable die parts and draw movements may be required. Complex tooling results in increased manufacturing costs and may result in increased production of scrap.
An undercut surface such as an undercut flange running along an edge of a trim piece may be especially difficult to manufacture. An undercut as used herein means that an outer-pointing normal extending outwardly at each point in the contoured surface swings from a first direction at one location on the surface to a second direction more than 90° away from the first direction at a second place on the undercut of the surface. For such a complex contoured surface wherein the undercut faces an opposite direction from the main portion of the Class A surface, a die-locked situation may be created. The least expensive and least complicated injection molding process utilizes straight-pull die movements. In a die locked situation, a portion of the mold metal would need to pass through a part of the injected plastic in order to be removed in a straight pull. Thus, undercuts typically require portions of the die to pull out in a sideways direction, perpendicular to the direction of a straight-pull. The side actions increase manufacturing complexity and cost. In a trim substrate having mounting extensions formed on the Class B surface that extend in a die draw direction, the conventional straight-pull molding tools could not accommodate such an undercut.